Project Summary Our long-term goal is to understand the molecular mechanisms causing human diseases associated with aging. One possible mechanism for age-related diseases is acceleration of the aging process by environmental and genetic factors. Our previous studies show that mouse models showing accelerated aging phenotypes are powerful tools to identify such factors. Recently, we have identified a spontaneous mutant mouse line, skt, that exhibits accelerated aging phenotypes including shorter life span, age-related retinal abnormalities including retinal degeneration, neurodegeneration in the hippocampus and increased inflammation in multiple tissues. By positional cloning, we have identified that a deletion mutation in the chondroitin sulfate synthese 1 (Chsy1) gene is responsible for accelerated aging phenotypes in skt mice. CHSY1 is a member of the chondroitin N-acetylgalactosaminyltransferase family that possesses dual glucuronyltransferase and galactosaminyltransferase activity and plays critical roles in the biosynthesis of chondroitin sulfate (CS), a glycosaminoglycan, that is attached to a serine residue of the core protein to form the chondroitin sulfate proteoglycan (CSPG). In the retina, CSPGs are abundantly observed in the area surrounding photoreceptor outer segments and the apical surface of retinal pigment epithelium (RPE). In our preliminary data, skt mice lack these CSPGs suggesting that CHSY1 is critical for generating CSPGs in these retinal areas. Furthermore, histological analysis showed that skt mice exhibit structural abnormalities in photoreceptor cell outer segments and apical processes of RPE cells, suggesting that proteins modified by CHSY1 are necessary to maintain the structural and functional interaction between photoreceptor cells and RPE cells. However, target proteins that are modified by CHSY1 and how those CSPGs function in the retina are largely unknown. The goal of this proposal is to understand the roles CHSY1 plays in the retina, and how a defect in this molecule causes accelerated aging phenotypes. Specifically, we will focus on investigating the role of CHSY1 in the interaction between photoreceptor outer segments and RPE (Aim 1), and identifying protein targets of CHSY1 in the retina by mass spectrometry analysis (Aim 2). Successful completion of this project will lead to identification of a novel mechanism associated with CS modification that regulates the normal aging process, and will contribute to better understanding of age- dependent diseases in the retina. It will also reveal novel biological/physiological functions for CS modification and CPSGs in vivo, which are poorly understood.